Magnetic recorder with automatic time delay between reversals of record transport system



Nov. 6, 1951 T. E. LYNCH 7 MAGNETIC RECORDER WITH AUTOMATIC TIME DELAY BETWEEN REVERSALS OF RECORD TRANSPORT SYSTEM Filed Jan. 51, 1946 4 Sheets-Sheet l INVENTOR.

Nov. 6, 195] T. E. LYNCH 2,574,218

MAGNETIC RECORDER WITH AUTOMATIC TIME DELAY BETWEEN REVERSALS OF RECORD TRANSPORT SYSTEM Filed Jan, 51, 1946 4 Sheets-Sheet 2 I N VEN TOR.

M [W BY v M Nov. 6, 1951 T. E. LYNCH 2,574,213

MAGNETIC RECORDER WITH AUTOMATIC TIME DELAY BETWEEN REVERSALS OF RECORD TRANSPORT SYSTEM Filed Jan. 31, 1946 4 Sheets-Sheet 3 IN V EN TOR.

T. E. LYNCH 2,574,218

H AUTOMATIC TIME DELAY BETWEE REVERSALS OF RECORD TRANSPORT SYSTEM Nov. 6, 1951 MAGNETIC RECORDER WIT 4 Sheets-Sheet 4 Filed Jan. 51, 1946 INVENTOR.

Patented Nov. 6, 1951 OFFICE .MAGNETIC RECORDER IWITH ,AUTOMATIC TIME DELAY QBETWEEN REVERSALS OF RECORD TRANSPORT SYSTEM iThomas Lynch, Cleveland, QOhio, assignor to ';The Brush "DevelopmentGonrpany; Cleveland, .0hio,-a corporation of Ohio ApplioationJanuary 31, 1946, Serial"No.-644,'598

.1- Claim.

This i-invention relates ;to magnetic recording and reproducing apparatus, .andzmore particularly to such apparatus :utilizing a as :a: magnetic recording medium azthirrflexibie magnetic record & member,;isuch. ,as'1a:wire filament or .tape, which may be stored OII'JI'BBISTOI, carrying ontmagnetic :recoriding and-reproducing:operations, although vsome oftthe features :of the .invention are of :broader scope.

Among ,the objects of .the.lnvention are novel magnetic recording devices-of; the :foi'egoingtype embodying warious novel 'features'which render them fooleproof and; simple t in operation; which eliminate 'difiicultiesi heretofore: encountered with such devices, .andxwhichiimproize their performance.

Theforegoing. an'drother objects of theinvention will be best understood from 'the following description: of exemplifications :thereof reference being had to. the accompany-ing drawings wherein Fig. :1 isna simplified:diagrammaticuview illustrating thev general relationship of the mechanical, magnetic and electric elements of a :-ma

netic recording and reproducing apparatuswexemplifying the invention;

Fig. 1 A .is'a diagrammatic-view similaratoiFig. -1 of a a modified iormofcdrive :control arrangementrbased onthe principles of the invention;

Fig. I B" is ardiagrammaticyiew similar to Fig- -l-'A of another drivecontrol-arrangement "exemplifying the invention;

' Figs. 'l-Can'd l-D are generallyidiagrammatic :side and plan yiews ofa modified-form of drive control arrangement'for a magnetic recorder of the type :showniin --Fig. 1;

Fig. 1 E f is a perspective 'view of some of the elements of -the control arrangement shown'in Figs. 1-0 and ?1'-D; and

Fig. 1 is an: electric circuit diagram showing the electric circuit connections --of all the elements of a practicalform of a recorder of the type described diagrammatically in connection with Fig. 1.

Fig. 1 illustrates inna simplified "diagrammatic manner: the generalarelatlonship of the mechanical, magneticand electric' elements of a magnetic recording and reproducing apparatus exemplifyingi thexprinciples of i the invention. A magnetic recording r medium in the "form of-a thin flexible :magnetic record :member, such as :a, magnetic record wire, jfilament or -wire-like tape, indicated "by :a dash-double-ddtiline 3 I .kis: arranged .to be --ree1ed T011" take-up reel 33 affrom :supply reel 34, "which are :shown drivenz-bwadlriva t-mechanism, includinga drive shaft 4--l3==:and:aidrive *$hait :rrndncin (operations carrier :th :control' {ci 2 -.4 .-:I.-4,:to:wh1ch- .thetatwo :-reels;533,:.34, Y respectively,

are coupled.

gIn j-the rspecific .garrangement asaseen in zFig. 1, magnetic recording and reproducing operations 5 areicarried on:whena,therrecording'rmediumfi iris impelled inthe'forward direction in'dicatedtby arrow ;;3 l-A by driving ;-and rotating reel 33,3 counterclockwise v.cdirection. In order :to play :back the :recorded 1 program or :to :make a mew ".I'BCOI'd on the .:recording medium .13 l 11311111151; the rewound v -on the rsupply :reel :34 which :is then -driven :and srotated 1in :clockwise direction, :as seen in Fig. ,1, the :directions :in which thewtwo rreelsare driven being indicated byarrowsaanplied l5 =tothe ;schematically indicated brake drums 52'-2;l associated with :the two-reels; .33, ;34, :respectively. .Inmoving jfrom cone-reel toward the other, the :recording 1 medium 3| is guided through '39, zimagnetic ,record:transducer head-structure 3.6 which operates to magnetically records-playback :as :well :as:eraserthe-signals recorded onthereccording-rmedium '3 I -In the particular arrange- .-;-ment ;shown,1the transducer :head is also utilized -for-level winding :the recording medium on the 25. reelgon' which (it :is reeled. ;The transducer fihea'd :structure 33.6 is not partof the invention and-may be: of the :type: described in theqcopending Begun "application Serial No. -.--.550,5'70, filed August 22, -11 944. :now abandoned, and its continuation-inmart-application -,Seria11- No. 1688,738, filed Au ust :16,-1946,issued,Ju1y- 4, .1950; as Patent No. 2,513;-

617, both assigned to The Brush Development Company.

:In order to simplify-the description of the cir- -cuits' -by. meansyof which the "recording, playback sand erasing operations :are performed, the -:ele- =-ments of the transducer head structure 36 are also indicated in the circuit diagram of :Fig. ,1, by :a 'dasheline rectangle 36,-A, andaisthere shown 40 providedr-with,,an erasing head 3'1, and -a record ..transduci-ng-head-.38. Each-of the.hea ds,31,38 'is shown-provided with windingsand a magnetic @core-structurewhich has pole pieces Separatedby ,za :non-magnetic i gap i-past which the recording ::medium :3 I :is *moving in :thedirection of the garrow 3 l-A. 'Therecording medium 3 I visaguided -.thr,o.ugh the transducer head structure so that iduri-ng'the recording operation eachelement of the'recording -medium rpasses successively first past the gaprregicnvof the r erasing head 31 :and

i-then "past; the gap region of a the record transa ducin'g, head-.38.

:Themecordin system;;shown :in .-F.i

arranged to carry on magnetic recording a r audible frequency range, good results are obtained by using a high frequency biasing flux of about 25 kilocycles per second and the same source of high frequency signals may be used for supplying a relatively large high frequency erasing current to the-erasing head 31 as well as of the selector switch 40 establish the recordin circuits when the contact blades are in position and they establish the playback circuits when the contact blades are in position 2.

When the selector switch is in the recording position I, its contact blade 40-3 connects a source of high frequency oscillations or an 050117, lator 4| to a source of positive power supply indicated by a plus sign, which is connected to the contact blade 40-3, the circuit as well as other analogous circuits described hereinafter being completed by the ground connections shown, to'which is also connected the negative terminals of all D. C. supply sources.

' The high frequency erasing current supplied by the oscillator 4| to the erasi'ng head 31 is of sufficiently large amplitude so that each longitudinal element of the thin moving magnetic recording medium 3|, passing the gap region of the erasing head 31, issubjected to an alternating flux strong enough to erase any previous magnetic signal records of the moving medium I and restore the magneticelements thereof to a magnetically neutral condition, After being sub- Jected to the magnetic erasing action by the eras- In Fig. 1, a conventionally shown microphone 42 serves as a source of the signals which are to be'recorded and a reproducing device, such as a loudspeaker 45 serves to reproducethe signals.

During a recording operation, the microphone is connected by way of contact blade 40-| to the input side of an amplifier 43, the output of which is supplied by way of contact blade 40-2 of the selector switch to the windings of the recording head 38 which records the signals, the circuits a being completed by the ground connections shown.

The high frequency bias component of the recording flux is supplied by a high frequency current component derived from the oscillator 4| by a circuit, such as shown, which includes an adjustable coupling condenser 44 for supplying an adjustable component of the high frequency oscillations to the output circuit of the amplifier 43where it is mixed with the amplified signal currents supplied by the microphone 42 and amplified by amplifier 43 and supplied thereby through its output circuit to the windings of the transducer head '38 which records the signals. The coupling condenser 44 and the other circuit elements of the system are designed to mix a suitable component of the high frequency oscillations derived from the oscillator 4| with the amplified signal current supplied by the microphone in such manner as to produce in the gap region of the recording head 38 the desired combination of the signal recording flux and the In general, when recording signals of the the small high frequency biasing component to the recording head 38.

To play back the magnetically recorded signals While the recording medium is moving in the same direction as during the recording process, the selector switch- 40 is actuated to the playback position 2. When the selector switch is in the playback position 2,its contact blade 40-3 disconnects the oscillator 4| from the source of power supply, thereby de-energizing the oscillator, and no highfrequency erasing or biasing currents are supplied to the erasing head 3'! and the transducer head 38. Furthermore, selector contact blades 40-|, 40-2 now connect the windings of the record transducer head 38, which operates now as a playback head, to the input side of the amplifier 43, the output .of which is now supplied after amplification in an additional amplifier stage "43-A to the reproducing device 45 for reproducing the. signals.

In the magnetic recording device shown in Fig. 1, the two reels 33,34 with the recording medium stored thereon form part of a self-supporting detachable guide unit 2-|0 designed for detachable interconnection with a motor or drive unit 4-l0. The drive unit 4| 0 is shown in the form of a casing in which are housed all the elements of the driving mechanism as well as the amplifier and the principal control elements of the device, and supplies the mechanical power required for reeling the magnetic recording medium from one reel to the other.

The drive mechanism of the drive unit 4-|0 has a drive motor 4-20 which may be provided with a built-in speed reducing mechanism so as to drive a motor drive shaft 4-22 at a speed at which it may be directly coupled to the drive shaft 4-l3 of the take-up reel 33 for driving it at the speed proper forcarrying on recording or reproducing operations. The driving mechanism of the recording-device shown is so designed as to assure that when one of the reels 33, 34 is driven forv reeling thereon the recording medium, the other reel will at all times be subjected to a braking action sufllcient to maintain the recording medium under tension, and that when the direction of the motion of the recording medium is reversed, the removal of the driving forces from one reel and the application to the other reel is controlled in a predetermind time sequence to assure that the two reels and the moving recording medium are first brought to a positive stop before the driving forces are applied to the other reel. The selective application of the driving forces to each reel is interlocked and subjected to the control of time action means so that whenever the application of the driving forces is reversed, the reel mechanism is first brought to a positive stop before the driving forces are applied to the other reel.

In the arrangement shown, the drive control mchanism includes coupling means, generally designated 4-30, for selectively coupling the motor drive shaft 4-22 either directly to reel drive shaft 4-l3 or through a speed step-up mechanism to the other reel drive shaft 4-| 4 for driving the supply? reel 34 in counterclockwise direction at an increased speed during the rewinding operation. I

the motor drive shaft 4-22 to the drive shaft 4-! 3 of the take-up reel, and instead couples the motor drive shaft 4-22 to gear4-36 of a train of step-up gears including gear 4-31, while the other coupling member 4-32, which is now in reverse coupling condition, couples the gear 4-31 to the rewind drive shaft 4-l4 for rotating the supply reel at a higher speed in clockwise direction.

' As shown in Fig. 1 the coupling member 4-3l is slidably keyed on an extension of the motor drive shaft 5-22 and is provided with a coupling disc 4-3 l-F having a peripheral row of one-way coupling teeth which establish coupling engagement with two complementary teeth of coupling disc 4-l3-F affixed to the reel drive shaft 4-l3, when the coupling lever 4-35 is in the forward drive position shown. When the coupling member 4-3[ is moved to the opposite rewinddrive position it breaks the coupling connection of the motor drive shaft 4-22 to the reel drive shaft 4-l3 and establishes instead a coupling connection between a similar row of one-way coupling teeth of its coupling disc 4-3I-R with the two complementary teeth of coupling disc 4-35-R aiiixed to the gear 4-36 which is revolvably mounted on the motor drive shaft 4-22. The gear 4-33 forms part of the drive-reversing and step-up gearing system including gear 4-3'! affixed to gear driven shaft 4-38 which is mounted coaxially with the reel drive shaft 4-l 4. The other coupling member 4-32 is slidingly keyed on the gear driven shaft 4-38 and is arranged to be slidably moved by the coupling lever 4-35 from the uncoupling position shown to the coupling position in which a row of one-way coupling teeth of its coupling disc 4-32-R establishes driving coupling engagement with two complementary teeth of a coupling disc 4-l4-R aiiixed to the reel drive shaft 4-l4 for driving it during the rewinding operation in the direction opposite to the direction in which the reel drive shaft 3-! 3 is driven.

The control lever 4-35 is shown pivotally mounted on a fixed pivot 4-4l and one end thereof is connected through a pivot pin 4-42 to a spring-loaded toggle arm 4-43, the other end of which is pivotally held on a fixed pivot 4-45. The toggle arm 4-43 is formed of two telescopically mounted sliding toggle arm sections, the ends of which are biased apart by a compression spring 4-46 so that when the coupling lever 4-35 is moved past a center position, its toggle arm 4-43 with its compression spring 4-4& will bring the coupling lever either to the forward coupling position shown or to the opposite rewind coupling position indicated by dash line 5-3 5-H.

The coupling mechanism of the type described may be controlled either mechanically or electrically. In order to provide for remote control, the coupling mechanism shown is electrically controlled. In the form shown, the electrical control comprises two relay or solenoid members 53-F, 53-R held in fixed position and having core or armature members which are pivotally interconnected to moving portions of the coupling lever so that when the forward solenoid 53-F is energized, the coupling lever 4-35 will be actuated from the dotted line position 4-35-R to the full line position shown,'and that when the rewind solenoid 53-R is energized, the coupling lever will be actuated to the dash-line position 4-35-R.

The drive control mechanism shown is arranged to utilize only a single time action means for assuring that whenever the drive control mechanism is actuated from either one or the other drive position to a standby position or to the opposite drive position, the time action means are actuated to make it impossible to establish the opposite drive connection until after a predetermined time action sufficient to assure that the reels have been brought to a stop before the opposite drive connection could be established, if the drive control mechanism is actuated to the opposite drive control position.

Fig. 1 illustrates in a simplified diagrammatic manner one form of such drive control arrangement. It utilizes as a time action means a single time delay relay 6!, which is arranged to open its contacts 62 instantaneously upon the de-energization of the relay and to reclose with a desired time delay when the relay is energized, or, in other words, to instantaneously open a control circuit and to close the control circuit with a required time delay.

The desired time action of relay 6| is supplied by an electronically controlled circuit including a condenser 33, a resistor 64 interconnected with a circuit which is controlled in such manner that the time required for charging the condenser to a predetermined potential determines a time delay which the relay 62 recloses while assuring that the relay opens instantaneously upon the application of a proper control action to the circuit.

In the arrangement shown, an electron amplifier tube 65 having an anode as well as a cathode 6! and a control grid 68 is utilized in a novel manner for controlling the operation of the time action relay GI, and the manner in which the condenser 63 is charged and discharged in order to provide the required time action in delaying the recloser of the relay as well as to assure that the relay is instantaneously opened depending upon the control action applied to the tube circuits. In the particular time delay circuit arrangement shown, the anode as well as its screen grid of tube 65 are interconnected to operate as a single anode electrode and are connected to a source of positive supply voltage indicated by 13+, one branch of the anode or plate circuit being formed by a resistance 69 and a resistance 1B serially connected between the anode of tube 65 and the'conventionally shown ground to which the negative terminal of the positive supply source B+ is also connected. The time action control condenser 63 is connected between the control grid 68 of tube 65 and ground and a grid resistor 64 is connected between the control grid and the terminal of the cathode 67. The relay coil BI is connected between the point of the interconnection of the two resistors 68 and 10 and the point of interconnection of the cathode 61 to the grid bias resistor 64 in such manner that when the condenser 63 is short circuited the current through the relay coil 6| will be instantaneously reduced town, and that when the short circuit connection isrremovedzfromthe'con- .denseri 63, .the' condenser 63 shall be charged at such slow rate as toassure that the current through the relay 6| reaches a valuesufficient to actuate'it to theoperatedposition only'after the required timedelay.

In accordance with the invention, the circuit elements of the time delay circuit arrangement shown are so chosen and designed that under equilibrium conditions when the condenser 63is fully charged and the-control grid is at zero bias voltage; with respect to the'cathode 61; the relatively large maximum value of the current flowing through the tube from the anode 65 to the cathode 67 and therefrom through relay coil 61 and the resistance Ill connected in series therewith tozground' at .a relatively large component of the voltage drop will be produced by its cur- .rent across the resistors 10 which completes .the energizingcircuit of the relay 6| to ground. With such circuit arrangement a momentary short circuiting of the condenser 63 willinstantaneous+ ly apply the very, high negative potentialdeveloped across the resistor 10 to the control grid 68 of the tube, and cause it to instantaneously stop the flow of the current through .the tubeand therelay coil BI and bring aboutinstantaneous actuation of the relay to the reversal blocking condition, which in the arrangement shown corresponds to the opening of the relay contacts 82.

According to the invention, grid resistance 64 is made sufiiciently large that when the short circuit of the condenser is removed the charge of the condenser 63 will build up gradually at a required slow. rate which will provide the proper time delay'before sufficient current flows at which the condenser 63 has restored thereto a charge which produces a current flow suiiicient to energize the relay 6|.

The time delay arrangement shown enables an extremely fast and fool-proof de-energization of the relay because the circuit elements of the system are so designed and chosen that when the-condenser 63 is short circuited the relaycoil 6| is connected across points of equal potential of two sides of a bridge connected between the terminal of the positive plate supply 13+ and the ground, one side of the bridge circuit leading from the B+ supply terminal to the anode of tube 65 and therefrom through the cathode 6'! by way of grid resistance 64 to the ground; the other-side of the bridge leading from the 18+ supply terminal through theseriesfifl and 10 to round.

In the practical time delay arrangement. ofithe type described above, very effective control action is secured by making the voltage drop across the tube 65 between the anode and the cathode 6! about of the voltage .drop across the elements formed bytherelay coil 6| and the resistor 60 through which the relay energizing current flows when the condenser is fully charged in its normal equilibrium condition.

In order to enable ready practice 'of .the invention by those skilled in the art and without in any way limiting the scope thereof, there are given below data of one practical form of time delay circuit arrangement of the type described above:

Tube 65 was a 6SJ7 tube. Condenser 63 was of- 'onem-f,

Grid resistor 64 was of 680,000-hms Resistor 69 was of 470,00Qohms. Resistor 10 was of 780009 11 1 In-the arrangement shown, the blocking potential is applied to the control grid 68o! tube by the operation of the selector switch 40 which is utilized to control the recording, playback as well as'the rewinding operations. Selector contact blade 40-4 applied a negative blocking potential to the control grid 63 whenever it is moved to or past position 3 from either one of its other positions I, 2 or 4,5. As a result, the relay opens each time the selector switch 40 is moved either from positions I and 2 toposition 3 or from positionsi and 4 toposition 3, or from either one of positions I and 2. to either one of positions :4 and 5, or vice versa.

As explained above, the reversal of the driving connection to the reels or, in general, to the impelling elements which impel the recording-medium, is controlled by the operation of thezselec tor switch 40 and particularly by its set of contact blades 40-3, 40-4, 40-5. The drive control cir-icuits also include a normally closed forward limit switch 5I-F which opens whenever the limit of the forward reeling motion is reached, a normally closed rewind limit switch 5l-R which opens whenever the limit of the rewinding operation is reached, a latch switch 53 which is biased to an open position and is closed only if the detachable reel holder and guide unit 2-; is latched in its coupled position to the guide unit 4-IO, and two auxiliary relays, namely, the forward relay 55-F and a rewind relay 55-11.

The drive control circuit further includes a set of switch control contacts Eli-F, Sl-F which are operated from their normal released position to the operative position shown when the coupling lever, or, in general, the coupling means, are actuated to establish a forward drive coupling connection and a set of similar switch contacts 56-12., 5'l-R which are operated from the normally biased position shown to the operative position when the coupling means are actuated to establish rewind driving connections. In the arrangement shown, the switches 55-5, SE-R control the selective energization and de-energization of the two coupling solenoids so as'to ole-energize the solenoid after it was energized to perform a drive reversal operation and after having performed its function in reversing the drive connection. The two other switches 51-F, B'I-R control the ener gization of the drive motor 4-20 and operate to assure'that the motor is de-energized during a drive reversal operation and to effect energization of the motor only when the drive reversing operation has reached a predetermined stage at'which the energization and driving action of the motor are desirable for performing the drive reversing operation.

In particular, the two sets of switches are shown controlled by a finger plate 4-49 suitably aflixed to the control lever 4-35 so as to move therewith and is provided with two sets of fingers 4-41, 4-48 for operating the two sets of coupling control switches 56-1 51-5, 55-R,51-R. The switches .SS-F, 51-F, 56-R, SI-R as well as the similar other switches shown are of the micro-switch type which operate with a snap action when actuated by a push pin or similar actuating element. In the arrangement shown, the several switches which are operated by the control lever 4-35, or, in general, the coupling control.means, are designed to operate in the fol-. lowing manner:

It is assumed that the-drive mechanism is in the condition shown inwhich the coupling mach anismestablishes the driving connectionmfrom U A. k

the motor 4-40 to forward drive reel shaft 4l3. In the arrangement shown, the reversal-of the drive connection is controlled by the selective closure of the contacts of either the forward drive relay 55-F or rewind driverelayfQSE-R, which also serve to control the energization' of themetor. The two auxiliary relays 55-1, 55-R perform merely the auxiliary function of makingit possi ble to separate the powerline c'ircuits whichsupply operating power for the motor 4-2 G and the coupling solenoids 53-F,- 53*-R-from the ope'ra'ting circuits which are used for remotely controlling the operation of the drive-mechanism and the 5 recording and reproducing operations-fro'mlow power relay supply sources which are indicated in the diagram by the plus sign and groundconnection.

With the mechanism in-thecondition-shown,- when the' contacts ofrewind-relay 55-R are closed, current will be sentfrom'oneterminalof; a source of power supplyindicated by a'double plus sign through the closed coupling interlocked contacts EB-R, and through the rewind solenoid Eli-R, "the energized circuit of which-is completed only if the time delay relay 5| closes its contacts which connect the circuit'to the positive terminal of the power supply'indicated' by a double minus sign. *Ihgfdouble plus and double minus signs are used for the sake of simplicity to indicate a conventional source of power which may be'either an alternating current source or a direct current source for supplying power to the motor and to the operating elements, such as the solenoids of the'coupling mechanism. I i

Upon energization, the rewind solenoid 53-R will start moving the coupling lever- 435 from the coupling position shown toward the dash-dot line position l---35-R. The two-couplinginter-' 4-32-R are sufiiciently engaged-and the coupling lever is past the over-center'position. The other set of coupling interlock switches'SS-F, S'I-Fare arranged to operate in an analogous manner when the forward solenoid 53-F is energized to operate the coupling mechanism to reverse the drive connection from rewind to forward drive.

With the foregoing arrangement, the drive mechanism will drive the recording medium in forward direction wheneverthe contacts of forward relay 55-F are closed, provided the coupling mechanism is in the-forward coupling position. Similarly, the drivingmechanism will drive the recording medium in the rewind direction when ever the contacts of'rewind relay eta-R, are closed, provided the coupling mechanism is in the rewind coupling position indicated by the dash-dot line 4*35-R.

The circuits controlled by the forward drive relay 55-F and rewind relay 55'R serve also to control the energization of the motor, 6-29 as well as the selective operationof the coupling reversing solenoids 53-F,- 53-R, as :a result the selective operation of the contacts of one or the other of the drive control relays 55+F, 55-R will also bring about a reversal of the coupling con-' nections of one or the other of the relay con tacts is actuated tothe closed position for driv-- ing the recording medium in one direction while the coupling mechanism is in a position in which direction.

it establishes a driving connection in the other Thus, if the drive mechanism is in the con dition shown in Fig. 1-in which the drive shaft of motor 428 is coupled to the drive shaft di3 of the take-up reel for driving it in forward direction-and the contacts of the rewind relay 554% are actuated to the closed position, it wiil complete a circuit leading by way of the closed coupling interlock contacts 56-R to the solenoid 53-R bringing about itsenergization, provided the contacts of the time delay relay 6| are closed. Thereupon, the rewind solenoid 53-R will be operated to reverse the coupling connection from the position shown to the position corresponding to the rewind drive position;

indicated by the dash-dot line l'35-R. When.

so actuated to the rewind position, the movement of the coupling mechanism automaticallyoperates the interlock contacts 56-R, ST-R. to

successively energize the motor and de-energiz'e the rewind solenoid 53-R as itreaches the rewind couplin position indicated by dash-dot line 4- 35-R..

In other words, the circuit leading to the twoselectively operating contacts of the forward drive relay 55-5 and the rewind drive relay 55-H- may be directly utilized for controlling the op eration of the drive mechanism to start and stop the driving action in one or the other direction or to at any time reverse the driving motion, in which case, however, the operation of the time action means 5i delays the reversal of the" driving connections until the mechanism has been first brought to a stop.

In the arrangement shown, the selective ac:

tuation of the forward drive relay 53-R, 53-1 is controlled by the operation of the selectorswitch blades 40-4, 4D5 by bringing them from a standby position 3 to any one of the forward drive positions I, 2 or to any one of the rewind minal of the relay supply source, through the" winding of the forward drive relay 55-1, through the contacts of 'the forward limit switch 51-5 to the normally closed contacts of the latch switch 53, and then through a common circuit portion leading to the contacts of contact positions 2, 4, 5 of the selector-contact blade 40-4,

as well as to the recording control switch 58' which is shown used to set the drive mechanism in motionfor forward drive during a recording operation.

Thus, with the arrangement shown, the forward drive 'relay 55-F will be energized and operated whenever the contact blades 46-5,

46 -4 are in'the "playback position! and alsof when they are in the recording position I, in

be controlledby the push-button drive switch 58 which may be combined with the microphone 42Isothat the person recording may-stopithej recording operation and start the recording operation as he transmits withrthemicrophone thev desired message. Inan analogous manner, the rewinddrive relay 55-3, will-.b e energized to operate, its contacts and cause the recording mediuni to be rewound wheneverthe selectorcon' tact blades 40-4, 40-5 are in either positions 4sor- 5.- a

Itwill be noted that when the selectorswitch 40 with its drive control blades is actuated from either one of-positions l, 2 to either one of positions '4, 5, or vice versa, contact blade 40-4, on reaching or moving past the standby position- 3, applies a blockingrpotential to the control circuit of time -delay relay 6|, thereby instantaneously causing it to open its contacts and. de-energize the operating circuits vofboth couplingsolenoids; Because of the time delayaction in reclosing its contacts, the time delay relay 6| will keep theenergizing circuitsofthe coupling solenoids 53-'F,, 53-R de-energized for the' time required in order-to bring the motor to a stop, whenever the selector switch 40 has-been actuated from either one of theforwarddrive positions I, 2 to either one of the rewind positions 4, 5, or vice versa.- I

"It will be noted that-whenever the selector switch blade 40-4 isyin the standby position 3 or is returned to the standby position 3 from any of the drive positions it will apply a-blocking potential to the control circuit of the time delay relay BI and instantaneously release its contacts to its normally open position inwhich it blocks the operation of the coupling reversing solenoids 53-F, 53-R. I I I I Instead of providing a separate, drive control switch 58 for driving the medium in forward direction or for'stopping it, the contact blade 40-4 of-the selector switch may be utilized to control the forward drive operation during the recording process by interconnecting the contact of its contact position I with the interconnected In suchcontacts of contact positions 2, 4, 5. case, it is merely necessary to remove the connection of the ungrounded terminal of the sound reproducing device 45 which, in the arrangement shown in Fig. 1, is connected by selector contact blade 40-4 in positionl to ground, so as to cut it ofi during the recording operation,

this being merely an auxiliary operation whichv can be performed in many other ways by other simple instrumentalities. I I I .The arrangement of the type described above makesit possible to discontinue at any time a. recording or playback operationand start a re-' winding operation by moving the selectorswitch from either one of positions I, 2 to either one ofpositions 4, 5, in which case the rewind operation will be started after the time delay provided by the time action of the time action relay 6|; Ina similar way, a rewind operationmay be discontinued at any time and changed over to arecording or playback operation by moving the se-- lector switch from any one of positions 4, 5 :to any one of positions l,.2, in which case the forward drive will be started after the time delay provided by the time action relay;6l to assure that the recording mediumandthe-Teels have been'first brought to a stop before starting tomove in reverse direction. W

It will be'noted that with thedrive mechanism in :the forward drive position shown, actuation of theselector switch from the standby position toany one of the forward drive positions I, 2 will was well as; the ;biasingc urrents, while at the same.

i spf iivad -h fli e' n d a nme delay. Similarly, in the event the drive coupling connection has been,previouslylreversedto estab by merely moving the; selector switch'from-the standby position to any one of the rewind posiu- ,H s.

The contact blades:of the selector switch 40, in addition to performing intheir difierent operating positions the vari us functions described above, are also utilized to perform additional opapplies theiull positive potential to the oscillator 4| for energizingit to supplysthe erasing as time thesource of positive supply which is connected to this s elector switchrblade is also connected through a voltage reducing resistance 13 tothe screen grid of a tube of-the additional amplifierstage 43 A,' -the reby reducing the anode current drain of this amplifier stage without in any way impairing theoperation of the principal amplifier-43 which serves :to amplify-the signal currents which are supplied to the recording head38. I v I II I I However, in the playback lwsi i'on 2 as well as in the rewind position 4, the selector switch blade 40-3 appliesthe full positive potential to-the screen grid of the additional amplifier stag'e 43-A so that the auxiliary amplifier 43-Aoperates with full efliciency Ago amplify the recorded signalsreproduced bythe transducer head 50 now operating asaplay'rback head to secure efiicient reproduction or therecord by' reproducing device 45. In the arrangement;s hown; the recordplaybackprocess 'isalso carried: on during the re winding operation for playing -back the recorded signal sequencein reverse direction. This is desirable: in manyapplications, because with a little experience, a user of such recording device will be able distingu and r co n z 1mm th -sc a bled sequence otthe recorded signals played back duringja rewinding operation one'or'another part of the previously recordedgmessage which he desires toplay back-.-; In such caserhehasmerely to during the rewinding process, selector switch blades 40-1, ',40-2 :compl'ete'yin; contact position 4 the'same,playbackcircuits'which they established :in position 2,;as described above;

Furthermore, selectorzswitch blade 40-l applies a 'groundc-conriection tothe-input side of the amplifier 43; when the selector switch is in the standby position or-in the special rewinding position 5 which may, be utilized for subjecting the recording, medium to a special'erasing operation, for instance, to, erasure by a direct current supplied to the recording-head, in which case the positive terminal; of a suitable direct current source is connected tothecontact element of contact position 5 of selector switch blade 40-2.

Instead of using time'action'means using electric circuit elementsfo'rdetermining the time delay; such as described above in'connection with the time delay relay 6 I other forms of time action means may be used. Thus, forinstance, a spring driven member, such as an arm of a spring-driven clock work, may be used as the timing element for interposing a required time delay each time a drive control action is performed ,for reversing the direction of the drive forces applied to the recording medium or a drive control action which might be followed by an action which results in the reversal of the driving forces applied to the recording medium, so as to prevent reversal of the driving forces applied to the recording medium before the recording medium was first brought to a stop.

Such modified time action means may be combined with a relay, such as relay Bl shown in Fig. 1, so that the time action means operates to reclose the relay contact with the required time delay, the relay contacts and the timing mechanism being combined so that whenever the relay winding i energized the contacts open instane taneously and at the same time cause the time action means to be charged for performing the desired timing action. Such time action relay means operating with a spring-driven timing mechanism are well known in the art and need not here be described. A relay 6| combined with such time action means may be controlled in the same manner as described above so that each time the selector switch is operated from a forward drive or rewind drive position to the standby position, the relay BI is energized t instantaneously open its contacts, the contacts being reclosed under the control of the time action means with the required time delay for restoring the conditions under which a reversal of the driving connection or, in general, a reversal of the application of the driving forces to the recording medium may be accomplished.

Instead of using a contact blade of a selector switch, such as selector blade 4ll4, for actuating the time action means to block a reversal of the driving connection each time the selector switch is actuated to reverse the driving connections, the time action means may be arranged to be operated each time the selector switch is moved from one control position to another control position for interposing a timed preventive action which prevents a reversal of the driving connection or, in general, a reversal of the driving forces applied to the recording medium until the end of the timing interval.

In Fig. l-A is shown one form of such modified drive control arrangement in which conventional. time action means are instantaneously actuated to the blocking condition in which it prevents the drive mechanism from completing a drive reversing operation during a predetermined time delay, whenever the drive control means such as selector switch d9, shown in Fig. 1, is actuated from any one of its operating to another operating condition. The rotary shaft of the selector switch 40 which carries the various contact blades 40l to 405 has also secured thereto an actuating member shown in the form of a cam sector 8| provided with a plurality of cam projections 82 arranged so that whenever the contact blades of the selector switch are moved from one position to the other, one or the other of the cam projections operates a suitably mounted switch 83. As indicated in Fig. l-A, the switch 83 serves to control the operation of time action means to instantaneously disable the drive reversing mechanism for the duration of a predetermined timing interval required to assure that upon performing a drive reversing operation, the recording medium is brought to a stop before driving forces are applied thereto in opposite directions.

As explained above the time action means may be a mechanicall timed. mechanism which is in- 14 dicatedin Fig. 1A as a dash-pot relay 6if arranged to instantaneously open its contacts 6l+-2 upon energization of the relay and t reclose its contact after a predetermined adjust ably set timing period following the re-energization of the relay. 7

The contacts 6l2 of the time action relay iiil may be connected in the control circuit leading from one terminal of an electric power source to the two coupling solenoids 53-F, 53-R so that each time the time action relay GI-l is encrgized it instantaneously opens its contact El 2 thereby disabling the coupling reversing mechanism for the period of the required timing interval.

,Alternatively, the cam projections 82 of the drive control selector mean 40 may be utilized for operating a mechanical latch member to interlockingly engage and look a mechanical element of th coupling mechanism each time such drive control selector is actuated from one operating position to the other, the time action means permitting the return of the latch member to the coupling releasing position only after the lapse of the required timing interval.

Instead of using a rotary drive control selector means of the type indicated in Figs. 1 and 1-A, push-button type control selector means may be used for controlling the operation of the drive mechanism. Fig. l-B shows a conventional type push-button mechanism which may be utilized for performing the control actions of a rotary selector of the type described in connection with Figs. 1 and 1-A. The selector mechanism of Fig. l.B may be provided with five push rods, only two of which are indicated at 85-4, 85-5, for performing the control action performed by the selector contact blades 4El4 and 405 of Fig. 1. The push rods 854, 855 are slidably guided in guide slits or holes of spaced mounting bars 86 which are joined by two cross bars 81 into a substantially rigid frame work. Each push rod is biased by a biasing spring 88 to the normal released positionin which all rods-except rod 85--are held. Furthermore, each push rod is provided with a laterally projecting cam-like latch projection 89 and passes through a longitudinal slit 9! of a latch bar 90, slidably mounted in slits or holes of the cross bar 81 of theframe work so that when any one of the push rods is. actuated from the released position to the operative position shown occupied by rod 85-5 the cam projectionof the actuated push rod will laterally displace or shift the latch bar 90 to release all other pushtrools, such as push rod 855 which is in the latch position, the latch bar 90 being returned by its biasing spring 93 to the latching position hown, thereby locking the operated push, rod in the operated position.

A selector control mechanism of the type shown in Fig. l-B may be provided with several sets of switches 95 one for each push rod and arranged so that when a push rod is actuated to the oper-- ated position shown occupied by push rod 85-5, itfwill actuate its set of switches to the operative position. The sets of switches operated by the several push rods of Fig. 1-3 may be utiilzed to perform the circuit control operations which are perforced in Fig. 1 by selector switch blades 40-4 to 40-5.

. The selector mechanism of the type shown in Fig. 1-3 is also shown provided with additional switch contacts '83l suitably supported on the frame work so that the switch 83l is operated byithe lateral movement of the push rod 90 each is: time one of the" other of he push 'butt6ris 85- -l 176 85 5 is actuated to ti-ie'operative osition- The additional switch 83I -maybe utili'zed forcontrollingthe time action means such as re- 16 siiifiiefit w bring 1 the coupling lever 4%3 5' mm"- th j forward drivefull lin'e' 'position shown to the dli$h"-'dot line-- rewind-drive position 4-35-12? 'I'h'e'connctor s'pring I I4' is similarlyeifective inla'y'-6'I- -I in'thesame manner 'as it is controlled 5' rturning' the coupling lever 4-'35"from the dash by the switch contacts 83 of the controlmechai ni's'm-shownin Fig. 1-A, for disablingth'e drive reversing mechanism during a predetermined timing interval, each time the drive control iifeiairis is-actuated from one operating conditionto'an other operating condition. The mechanical-M tion of the individual push rods of Y a-selector mechanism of the type shown in-Fig. l-B maybeutilized for-mechanically controlling the drive or dbt rewin'd dfive position' 435-R to the forward drive fullli'n position shown when the control lever IIIis returned from the dash-dot line position III-A to the full line position? 5; Means arealso provided for retaining or lockingthe-coupling control lever I I I, and preventing a revers'al of'th'e' driving forces applied to therecordin'g inedium, beforefirst bringing the re-' cording medium toastop. either in thefull'line the coupling mechanism of the type describedpositionshownto whichit'is brought for estababove'in" connection with Fig. 1 in whicli ca se the lateral movement of the'latch bar 90 may be utilized to movea-lock element into lockingengageinent with th e central portion of the con lisliing" the forward drive condition or the dashdotflineposition I I I -Ato' which it is brought for establishingthe rewind-drivecondition. The 1ockin means are shown in the form of two lockplin'g--le'ver-4'-35, preventingit from 'pe'rforming go ing projeiitlons 'II3' held suitably aflixed in the a drivereversing operation each time the selector means has been actuated from one-operatingoon dition' to another, the lockelement being in terconnected with time action means'wh'i'ch automa'nnerindicated'in Fig. 143 along the path of movement'of the handle arm lever I I I, so that it may be movedpast the interlocking projections H3 The portion'of the control lever II I is rematically return it to the coupling-release posi-* 2B sili'e'ntly flexible so that it may be lifted from its sion after a required time delay. I V

In Fig. 1-13 each set of switches 95 isshown" provided with releasable switch contacts 95'-5' which are closed only for'a'short instancewhen position'of locking-engagement with a locking projection-I I3 and moved from one position to the "other; The control arm of the control lever I II being biased to establish lockin engagement the associated push rod is actuated andpus'lied with a lookin p ol' n w e it iS moved beinwardly to the operated position at-the end of its inward stroke, the switch contacts 95 -5'being released to the open positionwhen the push rod isreturned by the latch bar 90 at the level'at which it holds the other switch contacts closed, in the manner'shown in Fig. l-B for the set of switches '95 of operated push rod 855. There lea'sable switch contacts 955 of the several sets of switches may be connected in parallel and- The drive control arrangement shown in Figs. 1 C-and 1E isalso combined with timeaction means operative to prevent a-reversal oi the application of the-driving forces to the recording medium before first stopping the recordin medium. In the'arrangement shown, there is" providedto this end a blocking member I I5 which is arranged to bernoved into a position in which used in lieu of the additional switch 83-I-' for -10 it blocks the movement of he coup level momentarily energizing the time action relay' BI--I each time one 'of the several'push rods'is operated to effect a drive control operation. V

In Figs. l-C to 1-E is shown a modified form of 4%35fro'm one"coupling position to the other whenever the "coupling control lever III is actuated from one control position to the other. The blockin'g'element H4 is combined with time drive control arrangement of the general type de- 'action means operative after the required time scribed in connection with Fig. 1. It has a coupling mechanism similar to that of Fig. '1, a couplin lever 435 serves to establish forward-drive coupling connections in the lull-line position delay to retract"blocking member H5 from the blockin position to a relea's'ing'positiori in which it permits thecouplingiever 4-35 to perform a drive reversing operation under the control of shown, and is movable therefrom to thedash-dbt-BOtheoontfol'l e line pisition 435'R, in which it establishesa re wind drive coupling connection during the rewinding operation; The coupling lever"435 isbiased by a toggle arm i -43 either to the forward-drive full line position or to the rewinddrive dashdot position 4-35-R in the manner described in" connection with Fig. 1. However, instead of operating the couplin 'control lever 4-35 through by solenoids, it is operated manually by means of. a control lever III pivotally mounted ona fixed pivot H2, and movable between'the full line position shown-to which it is brought for actuating the coupling mechanism to the forward-drive coupling "position-and the dash-dot line position I I I-A to which'it is brought for actuating the coupling mechanism to the-rewind drive coupling position.

As'indicated in Figs. 1-C and more control lever III 'isconnected to a movable portion oi." the coupling lever 4--35 by an energy'storing con nector element,'shown in theform ofia spring I I4'i'so that when the control lever I I I moved from'the full line position to the dash dot'position""II'I-A,' the 'biasingspring II4 will be" charged and 'tensioned so'that it'exertsa force'- InFig's. 1;-C- and'1-'D, the blocking member I I5 is shown held" by one arm of a rocking member IIIipivotally mounted on a fixed pivot Ill, and

carrying on its other arm a cam member II8, 5 shapedso that when the control lever III is moved'fro'm one'control position to the other control position a' portion thereof will engage the cam member H8 and actuate it to cause the rocker- II 6 to be rocked to a position in which its blocking member I I1 blocks the movement of the coupling lever 435"from one position to the other.

As indicatedin Figs. 1-C and 1-D, the rocker member H6 or the blocking mechanism is biased by a spring IZI to a releasing position in which the'coupling'lever 4-35 is free to 'be moved from one'coupling position tothe' other. In addition, the rocker-member has connected theretotime action" means, shown in the form' of a dash-pot I24,'which permits the blocking member III to 17 der the action of the biasing connector H4 of the coupling control mechanism.

The coupling-blocking rocker I I6 is also utilized to open the motor energizing circuit each time the drive control mechanism is actuated to reverse the direction of the driving forces applied to the recording medium. In the arrangement shown, this is accomplished by providing a switch I25 connected in the circuit leading from the drive motor l20 of the recorder so that each time the drive reversal blocking mechanism is actuated to the blocking condition, the motorcircult is opened, the switch I25 being re-closed only after the blocking mechanism, such as shown in Figs. l-C and 1-D, has been returned to its coupling-releasing position shown.

Fig. l-F is a circuit diagram showing all electronically operated elements or" a practical magnetic recorder designed for operation in accordance with the principles described above in connection with Fig. 1. In Fig. l-F, the block indicated by dash lines 2-40 represents the drive unit of Fig. 1; the block indicated by dash lines 4-H) represents the elements of the drive mechanism of Fig. 1; and the other circuit parts including the circuit part indicated by the dash double dot line block 43-0, the amplifier and control circuits of the recorder. The recording amplifier 43-0 has three amplifier stages associated with three amplifier tubes V-2, V-d, V-5. During the recording process, the tube circuit action of the amplifier leads from the plate or anode circuit of tube V-5 through the lead including resistor R-28 to a contact position I of contact blade 492 of the selector switch, in the manner analogous to that indicated diagrammatically in Fig. l. The amplifier stage associated with tube V-? corresponds to the amplifier stage 43-A shown in Fig. 1 and serves to provide the output required for playing back recorded signals with the reproducing device 45 or with the earphones which may be interconnected in the output circuit of tube V-l by means of a jack J-4. ,The D. C. plate current of proper voltage is supplied to the amplifier circuits by a power supply circuit including a transformer T-4 and 1 a two phase rectifier circuit includin tube V-! l.

The electrical wiring of the recorder is divided into several sections, namely, a wiring section shown in Fig. l-F, enclosed by the dash-line block 4ili of the drive and drive control mechanism, and a wiring section including the circuit interconnection between the elements of the recorder other than those of the reel holder unit 2-H] shown in Fig. 1-F. The wiring section of the drive mechanism 4-I0 is connected to the wiring section of the amplifier through cooperating plug and socket members 4-8fl, 4-8l in which are insulatingly mounted sets of cooperating contact elements shown marked by numerals l to I8, respectively, which automatically establish a circuit interconnection when the plu and socket members are brought into contact engagement.

In order to supply electric energy to the various elements of the recorder, the drive unit 4-40 is provided with a conventional power supply cord provided with a conventional terminal plug HID-T which is arranged to be plugged into a standard 110-volt A. C. low voltage power supply socket. The electric supply conductors connected to the plug-in terminal lllO-T lead through the wiring section of the drive unit 4-! to the primary winding of the transformer T-4 of the amplifier power supply. the circuit to the transformer in- 18 eluding a power supply switch lull-S and fuses IUD-F.

As indicated in Fig. l-F, the power supply transformer if-4 is provided with secondary windings i'or supplying heating current to the cathodes oi the several tubes V-2, V-4, V-5, V-t, V-l0, V-ll as well as for supplying heating current to the cathodes of the two amplifier tubes V-l, V-3 which form part of an oscillating circuit which serves as the source of oscillations indicated in Fig. 1 at 4!. As indicated in Fig; l-F, this secondary winding which supplies heating current to the cathodes is also utilized to supply energy to the three signal lamps, namely, the standby lamp I-i which, when energized, indicates that the power is on; signal lamp 1-2 which, when energized, indicates that the motor is energized and operates; and signal lamp 1-3 which, when energized, gives a warning that the recording medium carrying on a recording or playback process is approaching a predetermined part of its end, for instance, the last five minutes of its total recording or playback length, this signal lamp being operated by the warning switch 52-W oi the reel holder unit 2|0.

In order to carry on the magnetic recording process in a most efiective way, it is important to assure that when carrying on a recording operation, the level of the signal delivered to the recording head is sufficiently high so as to make use of the available dynamic range of the magnetic recording medium without, however, introducing distortion by an excessive level of the signal. A conventional electron-ray tube indicator is a particularly desirable medium .for indicating the level of the recorded signals, that is, of the recording current supplied to the recording head 38. In order to provide a level indication with an electron-ray tube indicator, its control electrode must be supplied with a D. C. voltage proportional to the signal, the level of which is to be indicated, and, in the past, a rectifier was generally used for deriving from the signal, the level of which is to be indicated, a D. C. voltage required to operate the electron-ray tube.

In accordance with the invention, the output amplifier tube which delivers the recording current, the level of which is to be indicated, is interconnected through a special circuit system with the electron-ray tube in such manner as to provide the desired D. C. control voltage without requiring a distinct rectifying unit, the rectification being supplied directly by the operation of the electron-ray tube. Fig. l-F illustrates one form of such electron-ray tube indicator arrangement of the invention.

The output stage of the amplifier which delivers the recording signal utilizes a high impedance signal source, namely, in the arrangement shown, the high impedance pentode tube V-5 for delivering the recording current. However, the impedance presented by the coil or windings of the recording head 38 to the high impedance source formed by the pentode is such that the voltage developed across the coil windings of the recording head 38 difiers in magnitude from the magnitude of the current delivered to the recording head.

According to the invention, novel circuit interconnections between a high impedance source of the recording current, such as presented by a pentode, and the voltage operated electron-ray tube with the current operated recording head, are arranged so as to derive a level indicating voltage component from the recording current The resistor elements R32, R33, R34 which are connected across the output side -of the 'pentode or screen grid tube V-5 and are interconnected with the screen grid of the tube, are so chosen and proportioned that they present thereto a relatively small impedance so that the voltage developed across the resistance elements R32, R33 is proportional to the current through the tube V-5 without, however, degenerating its operation.

A component of the voltage so developed across the screen grid of tube V-5 is impressed on the control grid 'of the electron-ray tube V-B through an input circuit including a series condenser C 22 and a shunt resistance R35 so preporti'oned that whenever the voltage 'a'pplied'to the control grid of electron-ray tube V-G becomes positive with respect to its cathode, the tube shall act as a rectifier and cause current to flow through the tube into the condenser (J-2'2. Furthermore, the condenser C 22 and'the resistor R35 are of such values that the voltage developed across the resistance R35 and impressed on the control grid of electron-ray tube V-6 by the charge on the condenser -22 does not diminish immediately to zero, but continues to be maintained by the current flow so as to exercise on the control grid of the electron-ray tube V-6 a control action corresponding to the magnitude of the plate current flowing in tube V-5.

In order to enable ready practice of this phase of the invention by those skilled in the art, and without in any way limiting the scope of the invention, there are given below data of one practical form of the combination of circuit elements required for securing the operation of an electron-rayindicator tube described above.

The pentode tube V-5-a 6SJ'7 tube.

The electron-ray tube V-6'-a 6E5 tube. Cathode bias resistance RSI-of 270 ohms. Plate resistance -R29'--of 10,000 ohms.

Plate resistance R-30of 15.000 ohms.

Screen circuit resistance R32-oi' 3300 ohms. Screen circuit resistance 1233-01? 3300- ohms. Screen circuit resl'stance-RSl-o'f 3300 ohms. Screen circuit resistance R35of one 'rnegohm. Control condenser -C-22-of 100,000 m. m. f.

The circuit diagram of Fig. l-F also discloses one form of a novel arrangement for providing a source of high frequency oscillations for supplying erasing current to the erasing head 31 anda high frequency A. C. bias component to thereto insure that the high frequency biasing currents are of'substantially sinusoidal wave form In. the

. 20 oscillator arrangement of the invention, high frequency oscillations of "excellent wave shape are obtained by the'coupling elements of the oscillator circuit associated with amplified tube V-I from the non-linear reactive elements of the coil of the recording head 38. In the oscillator arrangement associated with the amplifier tube V-l, this is achieved in the manner described below.

The output side of the oscillator tube V-l is connected to the control grid of the tube through a feedback circuit which includes only resistor and condenser elements arranged so as to form a phase shift network which shifts the phase of the output voltage required to maintain the tube V-l in an oscillating condition. the resistor and condenser elements of the phase shift network connected in the output circuit of tube V-l.

Furthermore, the resistor and condenser elements of the phase shift network are so disposed as to produce from the beginning to the end of the network a voltage of a progressively filtered and improved wave form of proper phase, which is impressed through feedback circuit connection including condenser 0-6 and grid resistor R-I to the control grid of oscillator tube V-I, thus assuring that the oscillations generated in the output circuit of this tube are of relatively Pure sign wave voltage, which is impressed through a coupling circuit including the resistor R-E onthe control grid of the amplifier tube V-S, which operates in the capacity of a power amplifier and supplies the amplified oscillator output of pure Wave form to the erasing head 3'! and the recording head 38 in the required proportions In accordance with the invention, the purity of the high frequency oscillator currents supplied in the windings of the erasing head 31 and recording head 38 is further improved by providing in their circuit connections to the output side or the oscillator amplifier tube V-3 a condenser C-ifl connected parallel to the coil of the recording head 38, the variations of which are so proportioned that they are resonant at the frequencies of the pure sign wave oscillations, and thus lowering their impedance at distortion frequencies. As a result, the coil windings of the erasing head '31 and the recording head 38 have the highest impedance at the frequency of the oscillations supplied by the oscillator, and they present an increasingly lower impedance at higher frequenones.

In order to enable ready practice of the invention by those skilled in the art, and without thereby limiting its scope, we are giving below data of one'oscillator arrangement of the invention which was used successfully in practice.

Oscillator tube V-l-a -6SJ7 tube Grid resistor R-i-l :me'gohm Plate resistor R-5'75,000 ohms Screen dropping resistor R"6-220,000 ohms Phase shift resistors Rr-l, -R-'8, each-'l50 ohms Screen by-pass condenser 'C-I-l0;000 m. m. f.

Phase shift condensers C-2, C-3, C-5, each-240 m. -m. f.

Feedback condenser C-5'l0;000 m. m. f.

Grid resistor 'R-l 0"220,000 ohms Cathode bias resistor R;-l3---330 ohms Coupling condenser C-ii l-lOOO m..m..f.

Condenser C-l2--1000 vm. .m. f.

Condenser 0-18-1000 111. m. f.

Winding of recording .head 38-impedance of 300 ohms and Q of 2.6 at 1000 cycles; impedance 91, 2,500 h s and Q of 3.3 at 10.000 y s.

The circuit diagram of Fig. l-F also discloses a novel electronic filter for the amplifier which is very desirable for the operation of recorders.

In the amplifier shown, the three amplifier tubes V4, V4, V-E are arranged to operate as a high gain resistance coupled pentode amplifier. The additional amplifier. stage of tube V-l is likewise resistance coupled to the output side of tube V45, and serves as an additional power amplifier stage during the playback process.

Wherever multi-stage amplifiers are used it is essential that cross-coupling between the amplifier stages shall be impossible or difiicult. This problem is generally solved by using de-coupling sections which introduce sufiicient impedance between successive amplifier stages so that crosscoupling becomes difiicult. Such de-coupling sections require many de-coupling elements including condenser elements of large capacity values and this is generally undesirable.

Furthermore, in providing power supplies utilizing amplifier tubes for deriving from an A. C. power supply a regulated D. C. voltage substantially free from A. C. component, it has heretofore been the general practice to provide an element, such as a gaseous tube, which serves as a reference voltage element in supplying the desired regulating action.

circuit connected between the output side of the full wave rectifier tube V-ll and the D. C. supply line conductors 300 and Ill-G includes'an amplified tube V-9 connected to operate parallel to the D. C. supply line, and an additional amplifier tube V-Ifi connected to operate in series with the D. C. supply line 300. The circuits of the two amplifier tubes V-9 and V-HJ are interconnected as two series stages of a cascaded amplifier with respect to any fluctuations in.the D. C. output voltage. In the circuit arrangement shown this is accomplished in the manner described below.

Any variation in the voltage across the D.. C.

' load presented by the amplifier is applied to the control grid of tube V-9 through a coupling condenser C-28. This voltage variation is reversed in phase and amplified by tube V-9, andis applied by the second coupling condenser C-Z'l to the control grid of the amplifier tube V-lll which is connected in series with the D. C. power supply line. Since the amplifier voltage variation has been reversed in phase from that originally appearing across the D. C. power supply, the series connected tube V-IO, which is controlled by this phase reversed and amplied voltage, will exert a compensating action on the current drawn by the D. C. supply line through tube V-IB from the rectifier V-l l, and this compensating action is magnified by the gain of the two tubes V-9, V-l operating as cascaded amplifier stages. Because of the cascaded amplifier action a very small variation in the voltage across the D. C. load will exert a very strong compensating control action thereby making it possible to obtain a 22 D. C. current supply of extremely great purity from A. C. voltage variations.

Furthermore, the electronic filter circuit shown is so arranged as to eliminate phase shift in its amplifier elements which might reduce the effectivness of the compensating control, and also by reducing to a minimum the number of circuit elements.

As shown in Fig. 1-F, to provide the bias for the series connected amplifier tube V-lfl a part of the drop in the low resistance R-52 and R-53 of amplifier tube V-9, which are connected parallel to the D. C. load, is applied through resistance R-54 to the control grid of tube V-IU; to provide the bias for the parallel connected amplified tube V-9 a part of the drop in the resistor elements R-55 and R-56, which are connected in series with the D. C. power supply, is applied to the control grid of the parallel operating amplified tube V-9. By deriving the bias voltages of the two electronic filter amplifier tubes connected in parallel and series with the load from the voltage divider action of a set of parallel connected resistor elements and a set of series connected resistor elements it is possible to exercise in the circuit a degree of D. C. voltage regulation without in the least degenerating or reducing the alternating voltage control.

The circuit arrangement shown provides also for an additional amount of D. C. regulation which will be now described. Thus, a change in the D. C. current through the series resistors R-55, R-5l applies to the control grid of tube V-9 a bias which produces in it a change in the plate current of such character as to supply in turn to the control grid of tube V-IU a bias voltagewhich produces the opposite effect, thus counteracting any changes in the D. C. current.

A D. C. power supply arrangement of the type described above, in connection with Fig. l-F, provides a high degree of A. C. voltage control which is almost perfect in suppressing A. C. voltage variations, while at the same time providing an amount of D. C. voltage regulation which is sufficient for application, such as amplifiers used in recording systems, through the D. C. regulation is not as large as that provided in properly designed prior art in electronic filter D. C. power supplies.

A D. C. power supply with an electronic filter of the type described above, in connection with Fig. l-F, when viewed from the amplifier, constitutes an A. C. impedance of such low valuethat it substantially eliminates any intercoupling effect between the amplifier stages without requiring the introduction of de-coupling sections in the amplifier stages. In other words, in a D. C. power supply provided with an electronic filter of the invention of the type described above, any A. C. voltage variations that may be impressed on the D. C. suppl connections to the amplifier will be suppressed because the extremely low impedance of the power supply to such A. C. voltage variations, while at the same time suppressing hum and operating with an extremely small amount of circuit elements.

In order to enable ready practice of the invention by those skilled in the art, and without in any way limiting its scope, there are given below data of one practical form of power supply of the type described above which was successful in actual use.

Parallel amplifier tube V-9-a 6SJ7 tube Series amplifier tube V-I 0-a 6V6 tube gala-1s screenurop iag resistance RI-E |of' phonemes Screen return resistance R'59-of 47,000ohr'ns" Plate resistance R52of 5,100 ohms Plate resistance R53of 100,000 ohms" Grid bias resistors R-55, R-'l, each-of 4'? ohms Grid bias resistor Rr54'-220,000' ohms Coupling condensers C41, C-28, each-10,000

m. m. f.

Filter resistor R-58-of 10,000 ohms Filter condensers 0-29, (J-30, each-4mpf.

Jack 3| providesfor connecting the plug leading from a so-called' battle-announce microphone'to the input side of the amplifier during a recording-process. A switch S4 is'shownconnected in the input circuit'to provide for proper gain for either radio or sound power recordings, the'switch being placed in the low gain position whenrecording from a radio source; For sound power recording, a switch S-lis placed inthe high gain position.

The amplifier'is also providedwith means for equalizing the response. The combination of the capacitor C| 9' and resistor B40 in the-plate circuit of amplified tube V- l provides for an increase in gain in the low frequency end of the spectrum both in recording and play-back. In addition, when the selector switch 00 in its playback position 2, the recording and reproducing head 38 is connected in parallel with the'condenser C4! to ground in order to boost the high frequency end of the frequency spectrum.

The recorder shown is designed to be eificient principally in recording speech. The equalization islimited to provide for essentiallyuniform response over a frequency range of 300 ,toapproximately 3700 cycles per second.

The expression magnetic record transducing as used herein inthe specifi ation and claimis intended to mean either the operation ofmagnetically recording signals on a magneticrecording medium, or the operation of reproducing magnetically recorded signals, or the operation of erasing magnetically recorded signals, or any combination of two or more of these operations.

It will be apparent to thoseskilled in the art that the novel principles of the invention disclosed herein in connection with specific exemplifications thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claim it shall not be limited to the specific exemplifications of the invention described herein.

Ina magnetic record transducing apparatus: a long magnetic record member; transducer means in magnetic flux linkage relationship with said record member; two rotatably mounted reels for storing the said record member; means for driving-said reels and said record member in forward and reverse directions; forward controlmea'ns forcontrolling said driving means to cause said reels and said record member to be driven in-the forward direction; reverse control'means for controlling saiddriving means to cause said reels and record member to be driven inthe reverse direction; interlocking means interlocking said forward control means with said reverse control means; first and second brake means, one for each of said two reels, for braking onlythe reelsupplying' the record member to the takeupj reel; three-position switch means having forward and reverse positions with an intermediate condition inbetween; electrical time delay meansconnected to said switch means and connected to said interlocking means and connected to said forward and reverse control means to block the application of reverse driving forces to the-supply reel when said reels are moving in the forward direction and to block the application of forward driving forces to the takeup reel when said reels are moving in the reverse direction, said blocking actions being removed immediately upon said reels coming to a. complete stop.

THOMAS E. LYNCH.

REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Number Name Date 789,330 Poulsen et al. May 10, 1905 1,237,496 T Fankhauser Aug. 21, 1917 1,552,321 Lea Sept. 1,-1925 1,592,613 Meyer July 13, 1926 1,634,979 Carter July 5, 1927 1,971,028 Bothe Aug. 21, 1934 2,051,787 Foster Aug. 18, 1936 2,231,365 Matthews Feb. 11, 1941 2,263,932 Schnoll Nov; 25, 1941 2,299,942- Trevor' Oct. 27-, 1942 2,300,632 Poch' Nov. 3, 1942 2,351,008 Camras June13, 1944 2,351,009 Camras June 13, 1944 FOREIGN PATENTS Number v Country Date 441,479 Great Britain Jan. 13,1936 

